Indicator control system for a train describer



Sept. 25, 1962 N. D. PRESTON 3,056,126

INDICATOR CONTROL SYSTEM FOR A TRAIN DESCRIBER Filed April 8, 1957 TRAIN CARRIED 2 Sheets-Sheet 1 TUNED COILS; r- E fi I- FIXED PICK-UP I-OOO TR RECEIVING COIL TUNER OSCILLATOR cRI ICRZ ICR3 ICR4 FIG.2. CODE TABLE I s I T IIa r q o I 234567898 RELAYCRI INVENTOR- RELIAYCRZ RELAY CR3 N.D.PRESTON RELAYCR4+++++----- BY 7 +=RELAY ENERGIZED =RE LAY DEENERGIZED s TTORNEY TUNED CIRCUIT ELEMENTS I rfi 33 I Fl F2 F3 F4 Sept. 25, 1962 D. PRESTON INDICATOR CONTROL SYSTEM FOR A TRAIN DESCRIBER 2 Sheets-Sheet 2 Filed April 8, 1957 FIG. I5.

MOTOR Ml MANUAL BLANKING 55 BUTTON INVENTOR. N. D. PRESTON H |S ATTORNEY United States Patent 3,056,126 INDICATQR CONTRGL SYSTEM FGR A TRAlN BESCRHBER Neil D. Preston, Rochester, N.Y., assignor to General Railway Signal Company, Rochester, N.Y. Filed Apr. 8, 1957, Ser. No. 651,425 1 Claim. (Cl. 340-316) This invention relates in general to an indicator control system for a train describer, and more particularly to an improved means for controlling the positions of a display indicating apparatus and for transferring a displayed indication from one unit to another in a train describer system.

In connection with various railway traffic systems, it is desirable to be able to display the identity of various trains either with respect to a particular location or in the order of their arrival at a certain station.

Although the present invention might well be applied to any number of such systems, for the purpose of this disclosure it has been shown as providing for the display of train identities as they pass a fixed wayside location in a train describer system. Such a system is particularly useful when employed at the approach to an interlocking area where the display of advance information as to the identity of each of the trains and their order of arrival facilitates the setting up of routes for such trains. Such a system calls for the automatic positioning of changeable indicators to display the desired letters or figures, transferring the data from one indicator to another, and blanking the indicators when the data displayed thereby is no longer useful. Among other things, it is desirable that the completion of initial posting, transfer, and wipe-out 0r blanking operations of the indicators shall be manifested by positive relay actuation so as to facilitate the automatic control of the indicator and also to betray faulty operation due to broken wires, bad contacts, and the like.

One object of this invention is to provide a novel circuit organization arrangement and interconnection of parts which cooperate to provide an improved control system for positioning a data displaying indicator.

Another object of this invention is to provide an improved positioning control circuit employing applied voltage increments for controlling the position of an indicator.

A further object of this invention is to provide a control system for positioning an indicator from a remote point employing a single positioning wire or bus.

A still further object of this invention is to provide an improved circuit arrangement for use in the control of a plurality of data displaying indicators to thereby position the same, to blank out their indications, and to cause a given position or indication to be read out from one indicator and transferred to another.

A still further object of this invention is to provide an improved indicator control system having a means for effecting a positive check on the integrity of the system.

Additional objects and advantages of this invention will be in part obvious from the accompanying drawings and in part pointed out as the description of the invention progresses and in which:

FIGS. 1A and 1B when placed side by side show a schematic organization of the circuit arrangement of the present invention; and

FIG. 2 illustrates a code table for controlling the indication to be displayed.

To simplify the illustration and facilitate in the explanation, the various parts and circuits constituting the embodiment of this invention have been shown diagrammatically and certain conventional illustrations have been used. The drawings have been made with the purpose 3,056,125 Patented Sept. 25, 1962 of making it easy to understand the principles and mode of operation rather than with the idea of illustrating the specific construction and arrangement of parts that would be employed in practice. The various relays and their contacts are illustrated in a conventional manner and symbols and associated with arrow tails and heads respectively indicate connections to the opposite terminals of a suitable source of power for the operation of the various relays.

Referring to FIG. 1A the inductive transfer equipment and organization is shown in block form and is briefly described herein because it is similar to that disclosed in the patent to H. C. Kendall et al., No. 2,693,525, to which reference is made for a more detailed description thereof. This drawing illustrates a track section T assumed to be in an approach to an interlocking area. A normally energized track relay TR is connected across the track rails near the entrance end of the track section. Each train approaching the interlocking area has mounted upon it one or more tuned coils, each resonant to a different frequency. Each train carried identity or control coil may comprise a number of turns of wire with a tuning condenser shunting the coil as diagrammatically illustrated in FIG. 1A. A fixed pick-up receiving coil is located at a convenient point adjacent the track section T. The fixed pick-up coil and train carried coils on each train are so mounted relative to each other that they will be brought into a suitably close inductive relationship as the train passes the identity detecting point. An oscillator is provided to energize the fixed pick-up coil and the oscillator is controlled by a conventional mechanical or an electrical tuner. The oscillator may be of any suitable type and may be adjusted to operate over any selected range of radio frequency. The tuned circuit apparatus F1, F2, F3 and F4 are respectively resonant at the various resonance frequencies of the train carried control coils. Associated with the tuned circuit elements are control responsive relays CR1, CR2, CR3 and CR4. Each CR relay can be energized only if a corresponding train-carried coil having a particular resonant frequency passes the fixed pick-up coil. With one or more tuned coils on each train, the passage of a train past the identity detecting point ca-uses one or more corresponding control responsive relays CR to be energized. The particular combination of energization for the total of the control responsive relays then determines the identity of the train that has passed the identity detecting point. For example, the receiving equipment may include four control responsive relays CR as shown in FIG. 1A, and with each train carrying one or more tuned coils, one or more of the respective control responsive relays CR is actuated as each train passes the identity detecting point. Since each of the four control responsive relays may be controlled to either an energized or deenergized condition for each separate identity, a maximum of 16 different combinations of pick-up and drop-away of these four relays can result. However, in the embodiments of the invention described here, only ten of the possible combinations have been utilized and all of the four control responsive relays CR1, CR2, CR3 and CR4 are normally dropped away as shown in FIG. 1A.

With reference to FIG. 1B the indicating apparatus F and S is assumed to be of the general motor-driven type as shown for example in the patent of Field and Hewes,

No. 2,731,632. However, the indicators described therein have been modified to provide an off-normal contact closed only in a predetermined blank position" of the indicator, and to provide an indicator with position contacts to take a form suitable for performing the function of a wiper or distributor arm cooperating with fixed contacts on a step-by-step voltage divider as schematically illustrated in FIG. 1B. The indicators F and S are further assumed to be of a type employing a rotatable drum such as D1 and D2 and having eleven different characters around the periphery thereof, namely, indication numerals 0 to 9 and a blank position B. These characters appear singly through a window W1 and W2 provided in each of the indicators F and S respectively. Wiper arms 20 and 21 are associated with the indicating plates or drums D1 and D2 respectively and rotatable therewith. The motors M1 and M2 as shown in FIG. 1B provide the driving force for the drums D1 and D2 and the wiper arms 20 and 21 respectively. Also associated with the indicator units F and S are voltage dividers DVF and DVS. The voltage divider DVF includes ten resistor taps or contact points, referred to as Ft) to F9, between the voltage dividing resistors therein. The voltage divider DVS includes ten resistor taps or contact points referred to as S0 to S9 between its voltage dividing resistors. The wiper arms 20 and 21 when rotated by their respective driving motors M1 and M2 successively contact the taps F0 to F9 and S0 to S9 respectively. A blanking contact FB on the voltage divider DVF, and a blanking contact SB is provided on the voltage divider DVS. The wiper arm 20 when in contact with the contact FB actuates a suitable off-normal contact arm L1. The wiper arm 21 when in contact with the tap SB actuates an off-normal contact arm L2.

Referring again to FIG. 1A, an input code voltage divider DVC is provided having ten voltage dividing resistors connected in series across a common direct current source. Ten code input resistance taps or contacts referred to as C0 to C9 are connected between the resistors to select a code potential in accordance with the condition of the relays CR as hereinbefore described.

A polar spring biased relay COR is associated with the position control circuit of indicator F and is so constructed as to be responsive to a potential of one polarity only. When the relay COR is in a deenergized position its contacts are assumed to be biased to the right-hand position by a suitable means such as, for example, spring 74. A relay ZCOR having identical operating characteristics to the relay COR is associated with the control circuit of indicator S and its contacts are biased to their right-hand position by a similar suitable means such as spring 75.

The output potential of the voltage divider DVC is assumed to be substantially equal to the output potential of the voltage divider DVF when a resistance tap of the voltage divider DVC as selected by the relay CR bears one reference numeral higher than a resistance tap of the voltage divider DVF as controlled by the position of the wiper arm 20. For example, if the potential output of the voltage divider DVC is determined by the selection of tap C6, the potential output of the voltage divider DVF is identical to DVC when the wiper arm 20 is in contact with the resistance tap F5.

The Winding of the relay COR is connected across the outputs of the voltage dividers DVC and DVF. The output of the voltage divider DVF in accordance with the position of the wiper arm 20 during operation is applied to the right-hand terminal of the winding of relay COR, and it is the polarity of the potential applied to this righthand terminal which applies the operating potential of the proper polarity to operate the relay COR. The potential applied to the left-hand terminal of the relay COR in accordance with one of the preselected resistor taps C of the voltage divider DVC is of the improper polarity required to operate the relay COR and is in effect a reference potential. The output potential of the voltage divider DVF must exceed the reference potential of the voltage divider DVC in order to operate the relay COR. It is necessary that the relay COR is capable of being operated by one voltage increment as determined by the resistance between each resistor tap of the voltage divider DVF. It is apparent from the preceding description and the accompanying drawings that the potential output of the voltage divider DVC increases with the reference value of the voltage taps C, that is, the potential output of the voltage divider DVC is greater when the control responsive relays CR select, for example, the resistance tap C8 than it is when the resistance tap C7 is selected; and the same condition exists with respect to the output potential of the opposite polarity of the voltage divider DVF, for example, its output potential is greater when its wiper arm 20 is in contact with tap F8 than it is when its wiper arm is in contact with resistance F7.

The winding of the relay ZCOR is connected between the voltage divider DVF in its read out position and the voltage divider DVS in its indicating position. The operating characteristics in respect to the applied potentials to the left-hand terminals of the winding of relay ZCOR by the voltage divider DVF and the applied potentials to the right-hand terminals of the relay ZCOR by the voltage divider DVS is similar to the cooperation between the dividers DVC and DVF with respect to the relay COR. it is assumed that a potential of the proper polarity applied to the right-hand terminal of the winding of relay ZCOR by the voltage divider DVS and having a value greater than the potential applied to the left-hand terminal of the winding of relay ZCOR by the voltage divider DVF is necessary to operate the relay ZCOR.

A posting relay OP is provided for initiating the operation of the indicator F and a similar posting relay ZOP is provided for initiating the operation of the indicator S. A wipe-out or blanking relay W0 is provided to cause the indicator F to rotate its drum D1 and its wiper arm 26 to the indication B and the relay 2W0 is provided to cause the indicator S to rotate its drum D2 and its wiper arm 21 to the indication B. A manually operated blanking button or wipe-out lever as shown in FIG. 1B is provided for operating the magnetic stick relay 2W0 to its right-hand position thereby cancelling or Wiping out the indication displayed on indicator S, which wiping-out action causes the drum D2 to display the indication B in the window W2. The wipe-out repeater relay WOl provides a means for transferring an indication displayed by indicator F to the indicator S when the indication displayed by the indicator S is manually wiped out by the blanking button.

FIG. 2 illustrates the code table employed wherein the various combinations of control responsive relays CR are in either an energized or deenergized condition to cause a distinct indicating numeral from 0 to 9 to be selectively displayed in a respective indicator.

At this point it is felt that this invention can be understood more fully by describing the operation of the various elements under an assumed operating condition. Assuming that both indicators F and S are displaying the indication B, and a train, carrying a plurality of the tuned coils approaches the identity detecting location on the track section T; and the identity of this particular train calls for the indication 6 to be displayed on the indicator; the relay CR2 becomes energized in accordance with the code table of FIG. 2 and in the previously described manner. When the train enters the track section T the track relay TR is deenergized. The picking up of the relay CR2 closes a circuit to the left-hand side of the correspondence relay COR from the resistor tap C6 which circuit extends from the tap C6 or" the voltage divider DVC and includes the back contact 23 of relay CR1, front contact 24 of relay CR2, back contact 25 of relay CR3, back contact 26 of relay CR4, wires 27, the asymmetric unit 28, and the winding of relay COR. The dropping away of the track relay TR closes a stick circuit through the lower winding of relay CR2 which extends from and includes the back contact 29 of the relay TR, the front contact 30 of the relay CR2, and the lower winding of relay CR2 to If a train of a different identity resulted in the picking up of another combination of CR relays the relay TR would provide a stick circuit for these respective relays as is apparent from 'FIG. 1A. The dropping away of the relay TR also provides the posting operation for the indicator F by a circuit which extends from and includes a back contact 31 of the relay TR, the front contact 32 of the relay CR2, wire 33, and the winding of relay to At this point in the operation of the indicator control system the output potential of DVC in accordance with resistance tap C6 as selected by the control responsive relays CR is applied to the winding of the relay COR; the relay OP is picked up by the previously-mentioned circuit and is held in a picked-up position by a circuit which extends from and includes contact 34 of the relay COR in its right-hand or deenergized position, the front contact 35 of the relay OP, and the Winding of re lay OP to With the relay COR in its right-hand position and the relay OP picked up, the wiper arm commences to rotate from its position B as shown in PEG. 1B. The rotation of the wiper arm 2t) is caused by the energization of the motor M1 by the completion of a circuit which extends from and includes the contact 36 of the relay COR in its right-hand position, the front contact 37 of relay OP, and the motor M1 to The picking up of the relay OP also connects the resistance elements of the voltage divider DVP in a closed circuit and inserts the extra resistor 38 in series with the indicating resistance elements by a circuit which extends from (I) and includes the front contact 39 of the relay 0?, the series of individual resistors on the voltage divider DVF associated with the indicator F, front contact 434 of relay OP, and the resistor to The rotation of the wiper arm 20 bythe motor M1 gradually increases the applied operating potential to the right-hand terminal of the winding of relay COR by the successive wiping of the contacts Ft) to F6 on the voltage divider DVP. The closure of the front contact 4% of the relay OP completes the circuit from the wiper arm 2% to the right-hand terminal winding of the relay COR in accordance with the particular position of the wiper arm 2% in respect to a particular tapped resistance element. It is readily apparent from the preceding description and the general principle and theory of operation of voltage dividers that as the wiper arm successively shunts out the resistors of the voltage dividing indicator the potential applied to the right-hand terminal of the corresponding relay is sucsively increased. As hereinbefore described, a reference potential has been applied to the left-hand terminal of the relay winding COR in accordance with the tap of the input DVC by the code selection means previously described. When the wiper arm 21] which is being driven by the motor M1 contacts the tapped resistance element F there is little or no potential drop across the relay winding COR. At this point as previously described the potential output of the input data voltage divider DVC and the voltage divider DVF are at equal resistance or an equal potential value above ground or It can readily be seen from FIGS. 1A and 113 that when the code calls for an indication 6 to be displayed on a respective indicator, there are four resistance elements between the positive terminal of the direct current source and the out put conductor of the voltage divider DVC to the lefthand terminal of the relay COR, and when the wiper arm 20 is connected with the tapped resistance element F5 there are four resistors between the positive connection of the direct current source and the right-hand terminal of the relay COR. When the wiper arm is driven by the motor M1 to the tapped resistance contact F6 21 potential is applied to the right-hand terminal of the winding COR having a value greater by one increment than the potential applied to the relay winding by the input data voltage divider DVC. This one voltage increment causes the re lay COR to operate, thus deenergizing and stopping the motor M1 by movement of contact 36 of the relay to its right-hand position. The deenergizing of the motor stops the wiper arm and the indicating drum D1 so that the indication numeral 6 is displayed in the window W1 of the indicator F. Simultaneously, with the energizing of the relay COR the stick circuit for the posting relay OP is open at contact 34 of the relay COR, the indication to be displayed by the indicators is caused by one voltage increment of the proper polarity applied to energize the polar relay COR. The potentials on each side of the re lay COR are substantially equal when the wiper arm 25 contacts a tapped resistance element of the indicating voltage divider DV F one numeral or character below the one to be displayed. It should he noted as previously described that as the wiper arm is progressively contacting the tapped contacts F0, F1, F2, F3 and F4 the potential applied to the left-hand terminal of the relay COR is greater than the potential applied to the right-hand terminal. However, as the relay COR is a polar operated relay responding to a potential of one polarity only, any reference potential supplied by the input voltage divider will not cause the relay COR to be picked up. The asymmetric device or rectifier 28 is inserted in the portion of the pick-up circuit for relay COR on the reference potential side of the relay winding for the purpose of preventing the undue energization of the relay COR during the time when the wiper arm 20 is rotating to increase the voltage increments applied to the right-hand terminal of the winding of the relay COR.

Transfer Control The operation of a typical train describer system contemplates a plurality of separate indicating elements to display the individual identity of particular trains in the order of their arrival at the identity detecting location. It is evident that a suflicient number of indicators must be included to adequately display the number of train identities corresponding to the largest number of trains that are capable of traveling at any one time between the identity pick-up point and the point where the identities are utilized and wiped out. However, for the purposes of this disclosure there are shown only two indicator units which are believed to sufiiciently illustrate the principles and organization of the present invention as utilized in a train describer system. However, it is assumed that a larger number of indicators will be required in actual practice. In the present disclosure when the indicator S is in the blank position the indication displayed by the indicator F is automatically transferred to indicator S. In accordance with the assumed operating conditions herein the indication 6 momentarily displayed on the indicator F is automatically transferred to the indicator S, if the indicator S displays the indication character B. The transfer control system herein utilizes the positioning or indicating resistance elements of the voltage divider DVF associated with the indicator F as the read out control for the indicator S.

The voltage divider DVF, with the relay OP deenergized, includes resistor 42 and excludes the resistor 38 in its series circuit, thereby conditioning the series portion of the voltage divider DVF to provide a reference potential to the relay ZCOR similar to the reference potential applied to the relay COR by the input voltage divider DVC.

Therefore when the indicator has posted the numeral 6 as previously described the relay OP drops away closing its back contacts 39 and 41 thereby providing a circuit for an input data reference potential of the voltage divider DVF to be applied to relay ZCOR by a circuit which extends from and includes resistor 42, back contact 39 of relay OP, the voltage divider resistances between the taps F9, F8, F7 and F6 on said voltage divider, the tapped contact F6 of the voltage divider, the wiper arm 20, back contact 41 of relay OP, the asymmetric device 43 and the right-hand terminal of the winding ZCOR. It should be noted that the back contact 40 of the relay OP is also closed which cuts out the resistor 38 thereby conditioning the circuit for the voltage divider in its read-out condition as hereinbefore described. The contacts of the magnetic stick wipe-out relays W and 2W0 are normally in their left-hand positions as shown in FIG. 1B. It should further be noted at this point that the off-normal contacts L1 and L2 are provided for operating the contact of relays W0 and 2W0 to their left-hand positions when the wiper arms 20 and 21 respectively are in contact with taps PB and SB respectively.

Assuming that the indicator S is in the blank or B position and the indicator F completes its operation to display the numeral 6 in its window W1, the indication is transferred to the indicator S after the correspondence relay COR has its contact operated to the left-hand position. The initiation of the transfer includes the picking up of the relay 20? by a circuit which extends from and includes front contact 65 of the off-normal contact L2, contact 48 of relay 2W0 in its left-hand position, contact 49 of relay COR in its left-hand position, front contact 47 of relay OP and the winding of relay 2GP to It should be noted that the relay OP must have suflicient slow release characteristics so that the aforementioned transfer circuit can energize the relay 201 before the relay OP is dropped away by the opening of contact 34 of the relay COR. When the relay 2OP is picked up it is held in that position by a circuit which extends from and includes contact 50 of relay ZCOR in its right-hand position, the front contact 51 of relay 2GP and the winding of relay 20F to The dropping away of the relay OP after the picking up of the relay 2GP conditions the voltage divider DVF of the indicator F to act as a read out indicator by the previously described circuits. The closure of front contact 52 of relay 2OP completes an energizing circuit for the motor M2 to drive the wiper arm 21, which circuit extends from 6+) and includes contact 53 of relay ZCOR in its right-hand position, front contact '52 of relay 20F and the motor M2 to The potential that is applied to the relay ZCOR by the voltage divider DVF is similar to the potential applied to the relay COR by the input voltage divider as controlled by the control responsive relays CR. The rotation of the wiper arm 21 increases the potential applied to the right-hand terminal of the relay 2COR similar to the manner in which the wiper arm 20 increased the potentials applied to the right-hand terminal of the relay 2COR. When the wiper arm 21 reaches the tap S6 of the voltage divider DVS associated with indicator S, the relay 2COR becomes energized thereby opening the previously described energizing circuit for the motor M2, thus stopping the movement of the indicator S. At this point the character 6 is displayed in the window W2 of the indicator S.

When the relay 2COR is energized, and prior to the dropping away of the slow release relay 201, a circuit is completed for operating the relay WO to its right-hand position which circuit extends from and includes contact 53 of relay 2COR in its left-hand position, the front contact 55 of relay 20F and the winding of relay W0 to The energizing of WO to this position completes a circuit for energizing the motor M1 which extends from and includes contact 56 of relay W0 in its right-hand position, back contact 37 of relay OP and the motor M1 to The energizing of the motor M1 causes the wiper arm 20 and the drum D1 to rotate until the character B representing a blank indication is displayed. When the indicator reaches the B position the off-normal contact L1 associated with the wiper arm 20 causes the closure of the front point 44 which operates the relay WO to its left-hand position by a circuit which extends from and includes front point 44 of offnormal contact L1, contact 45 of relay WO in its right hand position and the winding of relay W0 to At this point the indicator S is displaying the numeral 6 in acter B in its window W1.

Assuming that a subsequent train requiring the display of an indication numeral 3, for example, passes the identity pickup point before the train identified as numeral 6 in the indicator S leaves the area, the track relay is again deenergized. The control responsive relays CR2 and CR4 will become energized in accordance with the predetermined code thereby causing the indicator F to display the numeral 3 in the manner hereinbefore described. After the indication 3 is displayed on the indicator F it cannot be transferred to the indicator S because the front point 65 of the contact L2 is open thereby preventing the relay 20.? from being picked up as heretofore described. However, when the train identified by the numeral 6 in the indicator S leaves the area or the indication is no longer useful, the manual blanking or wipe-out lever is depressed which operates the relay W0 to its right-hand position by a circuit which extends from and includes contact 58 of the manual blanking button and the lower winding of the relay 2W0 to As the indicator F displays the numeral 3 the back point 88 of L1 is closed thereby permitting the wipeout repeater relay WOP to be energized by a circuit which extends from and includes back point 88 of L1, contact 98 of relay 2W0 in its righthand position, and the winding of relay NO? to Simultaneously with the operating of relay WOP to its right-hand position the motor M2 is energized by a circuit which extends from and includes contact 59 of relay 2W0 in its right-hand position, back contact 52 of relay 20F, and the motor M2 to When the wiper arm has rotated to the SB or blanking position of the indicator S, front contact 65 of off-normal contact arm L2 closes thereby Operating relay 2W0 to its left hand position by the previously described energizing circuit. The relay WOP is made slow-acting so that it will remain picked up during the crossover time of contact 98 of relay 2W0 from its right-hand position to its left-hand position. When the contact 98 of the relay 2W0 reaches its lefthand position the relay 2OP is energized by a circuit which extends from and includes back point 88 controlled by contact arm L1, the contact 98 of relay 2W0 in its left-hand position, the contact 46 of relay WOP, the back contact 47 of relay OP and the winding of relay ZOP to When the relay 2OP is picked up the indication numeral 3 displayed on the indicator F will automatically transfer to the indicator S in the manner previously described and the indicator P will be driven to its blanking position in accordance with the circuit organization hereinbefore mentioned.

Although the present disclosure shows the cooperation of the various elements herein including the voltage dividers, correspondence relays, and motors to rotate the respective indicator drums in a clockwise direction, it should be understood that the circuit arrangement can be readily modified to rotate the indicators in a counterclockwise direction without departing from the spirit or scope of this invention. Also, the embodiment of this invention utilizes a motor means to drive the indicators to the desired position. It should be readily understood that any other means, such as a stepping switch, can be readily utilized in its stead without departing from the spirit or scope of the invention.

What I claim is:

A system for posting coded information comprising:

(a) input means for selecting an input potential,

(b) a plurality of power driven posting indicators for selectively displaying different indicia,

(0) each of said posting indicators having a potential divider and a selector for selecting progressively different indicator potentials in said divider as the operation of the associated indicator progresses step-by-step for several steps,

(d) means controlled by said input means for initiating the power operation of a first of said indicators, (e) control means for comparing the relative potentials of said input potential and said indicator potential of said first indicator during the power operation of said first indicator, said control means being effective to stop the operation of said first indicator when a given difference in said indicator potential and input potential is reached,

(7'') means controlled in accordance with the cornpletion of operation of said first indicator for operating said second indicator to a position in correspondence with said first indicator provided that said second indicator is initially in a predetermined blank position, and

(g) circuit means responsive to the operation of said second indicator to a position in correspondence with said first indicator for operating said first indicator to a predetermined blank position.

References Cited in the file of this patent UNITED STATES PATENTS Winter May 8, Lewis Apr. 23, Hicks July 3, Hansell Jan. 11, Preston June 28, Tewksburgy May 4, Pouliart June 29, Montrose May 24, Herwald May 16, Nichols Jan. 20, Richardson Feb. 10, Kendall Nov. 2, Brixner Jan. 25, Field Jan. 17, Grubb Oct. 23, Frothingham Sept. 16, 

